U.S. Pat. Nos. 4,766,118 and 4,721,784 relate to benzoxazinyl-pyridazinone compounds, their uses and methods for making the compounds. Each of these patents discloses two reaction schemes for making 6-(3,4-dihydro-3-oxo-1,4(2H)-benzoxazin-7-yl)-2,3,4,5-tetrahydropyridazin- 3-ones.
In one scheme, the initial starting material is a 5-alkanoyl-2-aminophenol. The use of that starting material, which has the alkanoyl group at the 5-position, is required since the group is converted to the tetrahydropyridazin-3-one moiety in the final product and since the carbonyl carbon of the alkanoyl group becomes the carbon that is bonded to the 7-position of the benzoxazine moiety in the final product. This scheme, however, does not teach a method for preparing a 5-alkanoyl-2-aminophenol from a 2-aminophenol precursor. The use of such a precursor as the starting material would be advantageous over the use of the disclosed starting material since it would be less costly to prepare the final product from a simpler (i.e., less functionalized) starting material.
In the other scheme, the formation of the tetrahydropyridazin-3-one moiety's bond to the 7-position of the benzoxazine moiety is effected by acylating a benzoxazine intermediate. That intermediate, however, must be substituted at its 6-position since the acylation only takes place at the 6-position if the 6-position of the benzoxazine is unsubstituted. Consequently this scheme provides no means for synthesizing a compound having a tetrahydropyridazin-3-one moiety linked to the 7-position of a benzoxazine moiety without the latter moiety also being substituted at its 6-position. In addition, this scheme only discloses that the reaction for introducing the alkanoyl (acyl) group, which is ultimately converted to the pyridazinone moiety in the final product, takes place at a later step in the reaction scheme (i.e., after the formation of the benzoxazine intermediate).